Low cost high ductility cast aluminum alloy

ABSTRACT

An aluminum alloy for casting into a component, such as a vehicle component, is provided. The aluminum alloy includes 2 to 5 wt. % silicon, which is a lower amount of silicon compared to other aluminum alloys used for casting. The aluminum alloy further includes 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy. The aluminum alloy can further include 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy. After the casting step, the cast aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.

CROSS REFERENCE TO RELATED APPLICATION

This CIP Patent Application claims the benefit of U.S. patentapplication Ser. No. 15/061,257 filed on Mar. 4, 2016, entitled “LowCost High Ductility Cast Aluminum Alloy,” which claims the benefit ofU.S. Provisional Patent Application Ser. No. 62/134,072, filed on Mar.17, 2015, and entitled “Low Cost High Ductility Cast Aluminum Alloy,”the entire disclosures of the applications being considered part of thedisclosure of this application and hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates generally to an aluminum alloy for casting, amethod of forming the aluminum alloy, a vehicle component formed of thecast aluminum alloy, and a method of manufacturing the cast component.

2. Related Art

Casting of aluminum alloys is oftentimes used in the automotive industryto form lightweight components, including complex structural,body-in-white, suspension, and chassis components. There are many typesof known casting processes, for example high pressure die casting, lowpressure casting, and squeeze casting. The die is typically formed of ahardened tool steel. Although the casting equipment is expensive, thecost per component formed is relatively low, which makes the processsuitable for high volume production.

However, improvements to the casting process and materials used in thecasting process are desired. For example, an aluminum alloy capable offorming a component having higher ductility, without loss of fluidity orcastability, is desired. The aluminum alloy should also be resistant todamage associated with hot cracking, soldering, shrinkage, andcorrosion. In addition, although lightweight components are desired, thecomponents should still provide a high strength and toughness.

SUMMARY OF THE INVENTION

One aspect of the invention provides an aluminum alloy, comprising atleast 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. %manganese, based on the total weight of the aluminum alloy.

Another aspect of the invention provides a method of manufacturing acomponent. The method comprises casting an aluminum alloy, the aluminumalloy including at least 80 weight percent (wt. %) aluminum, 2 to 5 wt.% silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and notgreater than 0.6 wt. % manganese, based on the total weight of thealuminum alloy.

A method of manufacturing an aluminum alloy, comprising the steps of:melting a 300 series aluminum alloy; and adding silicon to the melted300 series aluminum alloy to form an improved aluminum alloy and so thatthe total amount of silicon present in the improved aluminum alloy is 2to 5 wt. %, based on the total weight of the improved aluminum alloy.The improved aluminum alloy further includes at least 80 weight percent(wt. %) aluminum, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, andnot greater than 0.6 wt. % manganese, based on the total weight of theimproved aluminum alloy.

The cast aluminum alloy is able to achieve a yield strength of at least110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and anelongation of 10 to 20%.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a graph illustrating the effect of silicon content on fluidityof an aluminum-silicon binary alloy;

FIG. 2 illustrates a portion of an example component formed of analuminum alloy according to an embodiment of the invention;

FIG. 3 is a photomicrograph of the component of FIG. 2;

FIG. 4 illustrates method steps used to form the component of FIG. 2according to an example embodiment;

FIG. 5 includes the composition of the aluminum alloy according to anexample embodiment of the invention and mechanical properties of castsamples having a 3 mm thickness and formed of that example aluminumalloy.

DESCRIPTION OF THE ENABLING EMBODIMENT

One aspect of the invention provides an improved aluminum alloy forcasting components, such as a lightweight automotive vehicle component,is provided. Examples of such components include structural,body-in-white, suspension, or chassis components. The aluminum alloyprovides a component with improved ductility and elongation, and withouthot tearing or loss of fluidity or castability. The aluminum alloy isalso less expensive than other aluminum alloys used for casting, whichis especially beneficial for high volume production.

The improved aluminum alloy is aluminum-based, and thus typicallyincludes aluminum in an amount of at least 80 weight percent (wt. %),based on the total weight of the aluminum alloy. In one embodiment, thealuminum alloy is formed by modifying a 300 series aluminum alloy. Aspecific example of the 300 series aluminum alloy is an A356.2 aluminumalloy obtained from recycled road wheels. The A356.2 aluminum alloyincludes 91.3 to 93.2 wt. % aluminum, not greater than 0.10 wt. %copper, not greater than 0.12 wt. % iron, 0.30 to 0.45 wt. % magnesium,not greater than 0.05 wt. % manganese, 6.5 to 7.5 wt. % silicon, notgreater than 0.20 wt. % titanium, not greater than 0.05 wt. % zinc,other elements each in an amount of not greater than 0.05 wt. %, andother elements in a total amount of not greater than 0.15 wt. %, basedon the total weight of the improved aluminum alloy. However, other typesof aluminum alloys could be modified to form the improved aluminumalloy.

The aluminum alloy also includes an amount of silicon (Si) which helpsachieve the improved elongation and ductility with reduced costs. Theamount of silicon ranges from 2 to 5 wt. %, based on the total weight ofthe aluminum alloy. This amount of silicon is reduced compared to otheraluminum alloys used for casting, which typically include 7.0 wt. % to11.0 wt. % silicon. The lower amount of silicon present in the improvedaluminum alloy creates a smaller eutectic phase, which leads toincreased elongation in the finished component, as the eutectic phase isone of the main limitations for elongation. The elongation of acomponent formed of the improved aluminum alloy with reduced siliconcontent is typically 10% to 20%.

The reduced amount of silicon also reduces the total cost of thealuminum alloy. The castability, strength, and toughness of the aluminumalloy can also be adjusted based on the amount of silicon. In addition,it has been found that the reduced amount of silicon does not sacrificefluidity or castability of the aluminum alloy, when compared to theother aluminum alloys which include 7.0 wt. % silicon or greater. Insome cases, the castability of the improved aluminum alloy is betterthan that of the other aluminum alloys including 7.0 wt. % silicon orgreater. Hot tearing is also avoided due to a lower amount of silicon.FIG. 1 is a graph illustrating the effect of silicon content on fluidityof an aluminum-silicon binary alloy.

Additional alloying elements can also be present in the improvedaluminum alloy to further improve elongation and ductility, or toachieve the desired strength and toughness. For example, magnesium (Mg),manganese (Mn), and/or iron (Fe) can be added to further improveductility, castability, strength, ductility, and/or toughness. Inparticular, the manganese can be used to prevent die sticking, and themagnesium can be used to form Mg₂Si for strengthening. The aluminumalloy can also include at least one of copper (Cu) and zinc (Zn) toincrease strength, preferably without negatively impacting corrosionresistance. The zinc is also used as a solid solution strengthener andto improve machinability. The additional alloying elements can provideother metallurgical effects as well, such as improved resistance to hotcracking, soldering, shrinkage, and corrosion. For example, specialproperties or other metallurgical effects can be achieved by titanium(Ti). Strontium (Sr) can also be added to modify properties that occurdue to the silicon. FIG. 2 illustrates a portion of an example component10 formed of the improved aluminum alloy, and FIG. 3 is aphotomicrograph 12 of a portion of the component 10 shown in FIG. 2.

According to one example embodiment, in addition to at least 80 wt. %aluminum and 2 to 5 wt. % silicon, the example aluminum alloy furtherincludes 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and notgreater than 0.6 wt. % manganese, based on the total weight of thealuminum alloy. The example embodiment can further include 0.01 to 0.07wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. %titanium, and less than 0.02 wt. % copper, based on the total weight ofthe aluminum alloy. Typically, the aluminum alloy includes at least 0.16wt. % iron, at least 0.3 wt. % manganese, at least 0.05 wt. % titanium,and at least 0.006 wt. % copper, based on the total weight of thealuminum alloy. The total amount of manganese and iron together ispreferably 0.6 to 0.8 wt. %, based on the total weight of the aluminumalloy. The manganese and iron can form an intermetallic phase thatprevents the alloy from attacking tool steel of a die, which istypically caused by iron. When the aluminum alloy is cast, the castaluminum alloy has a yield strength of at least 110 MPa, ultimatetensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to20%.

According to another example embodiment, the aluminum alloy consists of,or consists essentially of, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc,less than 0.5 wt. % iron, not greater than 0.6 wt. % manganese, and areminder of aluminum in addition to possible impurities. The impurities,if present, are in an amount not greater than 0.15 wt. %. This examplealuminum alloy could further consist of, or consist essentially of, theabove elements plus 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. %magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. %copper, based on the total weight of the aluminum alloy. The aluminumalloy could also consist of, or consist essentially of, the aboveelements plus at least 0.16 wt. % iron, at least 0.3 wt. % manganese, atleast 0.05 wt. % titanium, and at least 0.006 wt. % copper, based on thetotal weight of the aluminum alloy. FIG. 5 includes a specific examplealuminum alloy according to an embodiment of the invention. Thisaluminum alloy consists or consists essentially of 4.17 wt. % silicon,0.22 wt. % iron, 0.49 wt. % manganese, 0.4 wt. % magnesium, 1.35 wt. %zinc, 0.016 wt. % copper, 0.18 wt. % titanium, 0.06 wt. % strontium, anda reminder of aluminum in addition to possible impurities. Theimpurities, if present, are in an amount of not greater than 0.15 wt. %,based on the total weight of the aluminum alloy. A test was conducted todetermine the yield strength (YS), ultimate tensile strength (UTS), andelongation (%) of eight sample castings formed of the aluminum alloy.The castings each had a thickness of 3 mm. For the eight samples, theaverage yield strength (YS) was 116.43 MPa, the average ultimate tensilestrength (UTS) was 231.48 MPa, and the average elongation (%) was12.20%.

Another aspect of the invention provides a method of manufacturing thealuminum alloy. FIG. 4 illustrates steps of the method according to anexample embodiment. In one embodiment, the aluminum alloy is formed bymodifying a 300 series aluminum alloy. The aluminum alloy is preferableobtained from recycled wrought aluminum. A specific example of the 300series aluminum alloy is an A356.2 aluminum alloy obtained from recycledroad wheels. The A356.2 aluminum alloy includes 91.3 to 93.2 wt. %aluminum, not greater than 0.10 wt. % copper, not greater than 0.12 wt.% iron, 0.30 to 0.45 wt. % magnesium, not greater than 0.05 wt. %manganese, 6.5 to 7.5 wt. % silicon, not greater than 0.20 wt. %titanium, not greater than 0.05 wt. % zinc, other elements each in anamount of not greater than 0.05 wt. %, and other elements in a totalamount of not greater than 0.15 wt. %, based on the total weight of theimproved aluminum alloy. However, other aluminum-based materials thatcould be used to form the improved aluminum alloy are sold by CosmaInternational or Magna International, such as Aural-4. Manufacturing theimproved aluminum alloy from one of the recycled materials lowers theraw material cost, as it takes less energy to recycle an aluminum alloythan to create it from primary elements.

The method of forming the cast component typically begins by melting therecycled wrought aluminum, or other base aluminum alloy. The meltingstep can be conducted by an induction melter, or another source of heat.Once the base aluminum alloy is melted, the method includes addingsilicon to the melt and mixing the silicon with the base aluminum alloyso that the total amount of silicon ranges from 2 to 5 wt. %, based onthe total weight of the melted aluminum alloy, i.e. the final alloycomposition. The additional alloying elements, discussed above, can beadded to the melted mixture to form the improved aluminum alloy.Alternatively, the additional alloying elements could be present in thewrought aluminum or other base aluminum alloy. Once all of the elementsare mixed together, the aluminum alloy is ready for casting.

The method then includes casting the aluminum alloy which includes atleast 80 wt. % aluminum and 2 to 5 wt. % silicon, based on the totalweight of the aluminum alloy. As discussed above, according to oneexample embodiment, in addition to at least 80 wt. % aluminum and 2 to 5wt. % silicon, the example aluminum alloy further includes 1.0 to 2.0wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. %manganese, based on the total weight of the aluminum alloy. The examplealuminum alloy can further include 0.01 to 0.07 wt. % strontium, 0.05 to0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than0.02 wt. % copper, based on the total weight of the aluminum alloy.Typically, the aluminum alloy includes at least 0.16 wt. % iron, atleast 0.3 wt. % manganese, at least 0.05 wt. % titanium, and at least0.006 wt. % copper, based on the total weight of the aluminum alloy. Thetotal amount of manganese and iron is preferably 0.6 to 0.8 wt. %, basedon the total weight of the aluminum alloy. After the casting step, thecast aluminum alloy has a yield strength of at least 110 MPa, ultimatetensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to20%.

The cast component formed from the casting step can be, for example, acomponent for use in a vehicle. Any casting process used to formcomponents from an aluminum-based material can be used with the improvedaluminum alloy, for example high pressure die casting, low pressurecasting, or squeeze casting. In one example embodiment, the castingprocess is a die casting process, which typically includes forcing themolten aluminum alloy into an unheated die or mold cavity underpressure. The die is typically formed from hardened tool steel. Asdiscussed above, the castability and fluidity of the molten aluminumalloy with the reduced amount of silicon is equal to or slightly betterthan other aluminum alloys with higher amounts of silicon. The moltenaluminum is formed to a solid component having the shape of the mold,which can be a complex shape. Many different types of components can beformed by the casting process, for example, a structural, body-in-white,suspension, or chassis component. After the casting process, the methodcan include an optional heat treating process or other finishingprocesses. However, it has been found that a heat treatment process maynot be necessary when the component is formed from the improved aluminumalloy, which would provide the advantage of reduced process time andcosts.

The component formed from the improved aluminum alloy has improvedductility and elongation due to the lower amount of silicon in thealuminum alloy. In addition, the aluminum alloy can include additionalalloying elements to improve resistance to hot cracking, soldering,shrinkage, and corrosion, and also to achieve a desired strength andtoughness, or even higher ductility. As discussed above, the castcomponent formed of the aluminum alloy typically has a yield strength ofat least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, andan elongation of 10 to 20%.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings and may be practicedotherwise than as specifically described while within the scope of thefollowing claims.

What is claimed is:
 1. An aluminum alloy, comprising: at least 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy.
 2. The aluminum alloy of claim 1 including 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy.
 3. The aluminum alloy of claim 1, wherein the total amount of manganese and iron is 0.6 to 0.8 wt. %, based on the total weight of the aluminum alloy.
 4. The aluminum alloy of claim 1, wherein the alloy is cast and has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.
 5. The aluminum alloy of claim 1 including at least 0.16 wt. % iron and at least 0.3 wt. % manganese, based on the total weight of the aluminum alloy.
 6. The aluminum alloy of claim 2 including at least 0.05 wt. % titanium and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy.
 7. The aluminum alloy of claim 1, wherein the aluminum alloy is cast and formed into a component for a vehicle.
 8. A method of manufacturing a component, comprising the steps of: casting an aluminum alloy, the aluminum alloy including at least 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy.
 9. The method of claim 8, wherein the aluminum alloy includes 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy.
 10. The method of claim 8, wherein the aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20% after the casting step.
 11. The method of claim 8, wherein the aluminum alloy includes at least 0.16 wt. % iron and at least 0.3 wt. % manganese, based on the total weight of the aluminum alloy.
 12. The method of claim 9, wherein the aluminum alloy includes at least 0.05 wt. % titanium and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy.
 13. A method of manufacturing an aluminum alloy, comprising the steps of: melting a 300 series aluminum alloy; and adding silicon to the melted 300 series aluminum alloy to form an improved aluminum alloy and so that the total amount of silicon present in the improved aluminum alloy is 2 to 5 wt. %, based on the total weight of the improved aluminum alloy, and the improved aluminum alloy further includes at least 80 weight percent (wt. %) aluminum, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the improved aluminum alloy.
 14. The method of claim 13, wherein the improved aluminum alloy includes 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the improved aluminum alloy.
 15. The method of claim 13, wherein the improved aluminum alloy includes a total amount of manganese and iron of 0.6 to 0.8 wt. %, based on the total weight of the improved aluminum alloy.
 16. The method of claim 13 including casting the improved aluminum alloy, wherein the improved aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20% after the casting step.
 17. The method of claim 16, wherein the casting step includes forming the aluminum alloy into a component for a vehicle.
 18. The method of claim 13, wherein the improved aluminum alloy includes at least 0.16 wt. % iron and at least 0.3 wt. % manganese, at least 0.05 wt. % titanium, and at least 0.006 wt. % copper, based on the total weight of the improved aluminum alloy.
 19. The method of claim 13, wherein the 300 series aluminum alloy includes 91.3-93.2 wt. % aluminum, not greater than 0.10 wt. % copper, not greater than 0.12 wt. % iron, 0.30 to 0.45 wt. % magnesium, not greater than 0.05 wt. % manganese, 6.5 to 7.5 wt. % silicon, not greater than 0.20 wt. % titanium, not greater than 0.05 wt. % zinc, other elements each in an amount of not greater than 0.05 wt. %, and other elements in a total amount of not greater than 0.15 wt. %, based on the total weight of the improved aluminum alloy.
 20. The method of claim 13, wherein the 300 series aluminum alloy is obtained from recycled road wheels. 